1. Field of the Invention
The present invention relates to a method of designing a piezoelectric component used as a ladder filter, an oscillator, a discriminator, or other electronic component. More particularly, the present invention relates to a method of designing a piezoelectric component in which a piezoelectric element and a terminal are secured in position by a holding pressure applied in the thickness direction.
2. Related Art
Typically, in such a piezoelectric component, a piezoelectric resonator, a terminal, and a spring member are contained in a case. The piezoelectric resonator and the terminal are held by a holding pressure which is applied in the thickness direction and generated by the spring member. Further, the interior of the case is sealed by providing a lid including a resin permeation prevention sheet and a resin at the opening of the case. The piezoelectric resonator and the terminal are electrically connected to each other by the holding pressure applied by the spring member.
Such a piezoelectric component inevitably experiences variation in the thickness of the piezoelectric resonator, the terminal and the spring member and the variation of the interior-dimension of the case.
Therefore, if the variation of the dimensions of each of the piezoelectric resonator, the terminal and the spring member is small, a contact pressure (holding pressure) of the piezoelectric resonator and the terminal becomes small. As a result, poor connection occurs and the reliability of the shock resistance is greatly decreased.
On the other hand, if the variation of the dimensions of each of the piezoelectric resonator, the terminal and the spring member is large, a contact pressure (holding pressure) of the piezoelectric resonator and the terminal becomes large, and thereby the assembly of the component becomes very difficult. Further, there is a problem that an electric characteristic is deteriorated because of too much damping of the piezoelectric resonator.
To overcome the above described problems, conventionally, the contact pressure is stabilized by making uniform the thickness of the components contained in the case via lap polishing of the piezoelectric resonator or aligning the thickness of the terminal when forming thereof.
However, in the above described methods, the alignment process is very expensive and requires great effort.
To overcome the above described problems, preferred embodiments of the present invention provide a method of manufacturing a piezoelectric component which reliably and consistently achieves an appropriate contact pressure even if the variation of the thickness of the components constituting the piezoelectric component occurs.
According to a preferred embodiment of the present invention, a method of manufacturing a piezoelectric component includes the steps of providing a case having an opening, placing a piezoelectric resonator in the case, arranging a terminal including a external connecting portion to extend from the opening of the case toward outside of the case, and arranging a spring member in the case so as to maintain contact with the piezoelectric resonator and the terminal in the thickness direction, and designing the spring member such that the piezoelectric resonator and the terminal are held by a holding pressure in a range not larger than Fmax when a spring height is Smin and not smaller than Fmin when a spring height is Smax, where a thickness range of the piezoelectric resonator, the terminal and the spring member is not smaller than the minimum value of Tmin and not larger than the maximum value of Tmax, a dimension range of the case interior is not smaller than the minimum value of Wmin and not larger than the maximum value of Wmax, a permissible holding pressure range of the piezoelectric resonator and the terminal is not smaller than the minimum value of Fmin and not larger than the maximum value of Fmax, Smin is the spring height when the thickness of the piezoelectric resonator, the terminal and the spring member is the maximum value of Tmax and the dimension range of the case interior is the minimum value of Wmin, and Smax is the spring height when the thickness of the piezoelectric resonator, the terminal and the spring member is the minimum value of Tmin and the dimension range of the case interior is the maximum value of Wmax.
According to another preferred embodiment of the present invention, a method of designing a piezoelectric component which includes a substantially box-shaped case having an opening, a piezoelectric resonator contained in the case, a terminal including a external connecting portion extending from the opening of the case toward an outside of the case, and a spring member contained in the case and arranged to maintain contact with the piezoelectric resonator and the terminal in the thickness direction, the method including the step of designing the spring member such that the piezoelectric resonator and the terminal are held by a holding pressure in a range not larger than Fmax when a spring height is Smin and not smaller than Fmin when a spring height is Smax, where a thickness range of the piezoelectric resonator, the terminal and the spring member is not smaller than the minimum value of Tmin and not larger than the maximum value of Tmax, a dimension range of the case interior is not smaller than the minimum value of Wmin and not larger than the maximum value of Wmax, a permissible holding pressure range of the piezoelectric resonator and the terminal is not smaller than the minimum value of Fmin and not larger than the maximum value of Fmax, Smin is the spring height when the thickness of the piezoelectric resonator, the terminal and the spring member is the maximum value of Tmax and the dimension range of the case interior is the minimum value of Wmin, and Smax is the spring height when the thickness of the piezoelectric resonator, the terminal and the spring member is the minimum value of Tmin and the dimension range of the case interior is the maximum value of Wmax.
In preferred embodiments of the present invention, the spring may have linear spring characteristics or non-linear spring characteristics.
Also, it is preferred that the variation range of the dimension of the component and the interior of the case, in other words an admissible range of the spring-height Smin-Smax should be wide.
In addition, the variation of the pressure applied by the spring member when the spring height is low is preferably small.
Further, the original spring height should be low in view of the assembly and the size of the product.
In preferred embodiments of the present invention, the spring can be made of material which is different from that of the terminal. Alternatively, the same material can be used for the spring member and the terminal. For material having a spring characteristic, elastic bodies such as rubber can be used instead of a plate-shape metal spring.
Other features and advantages of the present invention will become apparent from the following description of the invention which refers to the accompanying drawings.